In generally known hydraulic ratchet wrenches with double-action hydraulic cylinders, a piston is movable within the hydraulic cylinder as a disk piston with a piston rod tightly protruding from the hydraulic cylinder for ratchet actuation. Within the hydraulic cylinder, the displaceable piston constitutes a working stroke chamber as a high-pressure chamber on one side of the piston, and a return stroke chamber as a low-pressure chamber on the piston side with the piston rod.
The known hydraulic ratchet wrench furthermore comprises a two-phase hydraulic pump arrangement with a gear pump and a piston pump. The gear pump and the piston pump are driven by means of a pump motor controlled by pump motor controls via the pump motor's drive shaft. Thus, thanks to its construction, the gear pump is able to pump hydraulic oil with relatively high conveying capacity per motor revolution, up to a pressure of about 100 bar. The piston pump, on the other hand, is able to pump a relatively lower quantity of hydraulic oil per motor revolution, however at considerably higher pressures. The pump arrangement is connected via hydraulic controls to the working stroke chamber and the return stroke chamber.
This known pump arrangement is controlled by the hydraulic controls so that in the first phase of a wrenching process, when still no or only little torque is to be provided in the ratchet unit, the working stroke chamber is filled by the gear pump pumping rapidly and with high conveying capacity. In a second phase, towards the end of the wrenching process, when a high wrenching torque is to be produced, the hydraulic controls disengage the gear pump and engage the piston pump, so that the latter pumps with greater pressure into the working stroke chamber. The switchovers in the hydraulic lines required for this (in particular the switchover of advance and return at the hydraulic cylinder stroke chambers) is effected by expensive, break-down prone valves, in particular by solenoid valves requiring their own supply of energy. As a result, the energy requirements are relatively great for the installation, in particular for the drive motor. This in turn leads to unfavorably great heat production in the hydraulic oil. It is therefore necessary, in these known systems, to cool the hydraulic oil with expensive coolers and/or to use heavy and large oil tanks with a large volume of hydraulic oil, thus rendering operations more difficult.
It is the object of the present invention to further develop a hydraulic ratchet wrench of this type with a double-action hydraulic cylinder drive so that an economic, reliable and simple design, together with lower weight, smaller dimensions and low energy consumption is possible.